Click on the link:
Two easy ways:
1. Click on the "Blending mode" dropdown selector above the layers channel (next to the opacity and fill options). Select Overlay there.
2a. Right click on the layer you wish to apply it to, and select "Blending Options...". (2b) In the next pane you can select the blend type as before, but you have more control over other aspects of the blending as well.
Hope this helps!